Method for the cyanoethylation of cotton textile fibers



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United States Patent 2,857,239 Patented Oct. 21, 1958 nice METHOD FGR THE CYANOETHYLATION OF CGTTQN TEXTILE FIBERS Norbert M. Bikales, Stamford, Conn, assignor to American Cyanamid Company, New York, N. Y., a crporation of Maine Application June 30, 1955, Serial No. 519,050

2 Claims. (Cl. 8-120) This invention relates to a process of cyanoethylation of alpha-cellulose, andparticularly to the cyanoethylation of cotton.

The standard procedure for the cyanoethylation of cotton and other types of cellulose involves two steps. The cotton is first treated. with a dilute solution of strong alkali. such as caustic soda. Two percent is a common concentration. After the alkali treatment, excess alkali is mechanically removed until the cotton retains only a moderate amount of solution, for example from 50- 100% of its weight. This material is then treated with a very large excess of acrylonitrile, for example ten times the weight of cotton, at somewhat elevated temperatures, for example from 50-60 C. Cyanoethylation results, introducing sufiicient cyanoethyl groups so that the beneficial properties are obtained. The extent of reaction is normally measured by percent nitrogen. in the, final product. Percent of nitrogen from 2%. to 7 is obtained. While the product is of excellent quality, the cost is markedly increased by two factors, both of which result in added consumption of acrylonitrile. The first factor, and in many operations the most important factor, involves a mechanical loss because of the large excesses of acrylonitrile used. There is also a tendency for the, formation of by-products such as B,B'-oxydipropionitrile and the like, which further increase the consumption of acrylonitrile. The efficiency of utilization of acrylonitrile is normally measured by the so-called acrylonitrile ratio, which is usually abbreviated as the AN ratio. This abbreviation will be used throughout the specification. The AN ratio is often as high as 5, that is to say five times as much acrylonitrile is lost as is fixed in the form of cyanoethyle groups on the cotton or other cellulosic material. Improved processes have brought the AN ratio to around 3. Another disadvantage to the standard two-step process is the necessity for handling relatively large volumes of liquid so that the output of a given piece of equipment is markedly reduced.

In the past it has been proposed to cyanoethylate ligno cellulose paper pulp in order to produce a product for use as an insulator and dielectric capacitor. This process is described in the patent to Miller and Flowers No. 2,535,690 and utilizes a single-step process with a very large excess of sodium hydroxide solution and a small amount of acrylonitrile. In general the amount of sodium hydroxide used is in excess of twenty times the weight of cotton. The acrylonitrile used is considerably less than the cotton. Only a rather small amount of cyanoethylation results, corresponding to a nitrogen content of about 2.8, which cannot be exceeded. The patentees state that the greater degree of cyanoethylation renders their product useless.

When the Miller and Flowers process is used with alphacellulose such as cotton, cyanoethylation takes place, but the qualities of the cotton are not useful. Thus, for example, the tensile strength is inadequate. The AN ratio is also fairly high, about 3.5. As a result the Miller and Flowers process has not been practical for the cyanoethylation of alpha-cellulose, such as cotton.

According to the present invention, it has been found that under certain very specific conditions, it is possible to cyanoethylate alpha-cellulose, such as cotton, in a ingle bath containing a large amount of caustic alkali and a small amount of acrylonitrile to produce a prodnot which usually shows increased tensile strength and improved resistance to heat degradation and which resists the attack of microorganisms to a greater degree than untreated cotton, although it is not completely mildewproo-f, as is cotton cyanoethylated by the usual processes.

The first of the conditions which are essential is the temperature. The temperature should not exceed 20 or be lower than 10 C. and is preferably around 15 C.

A concentration of sodium hydroxide must be maintained between about 8 and 12%. The ratio of sodium hydroxide solution to cotton or to other alpha-cellulose must not exceed 14:1. The ratio of acrylonitrile to cellulose will vary from a low of about 1 part acrylonitrile to 4 parts of cellulose up to about 1:1. Larger amounts of acrylonitrile do not seriously interfere with the process, but no improvement in product is obtained, and the loss of acrylonitrile as measured by the acrylonitrie ratio rapidly mounts. Incidentally, in the present specification, the acrylonitrile ratio is determined in a s ightly different manner than with ordinary cyanoethylation. Because of the relatively small amount of acrylonitrile present in the bath, it is impractical to recover it, and therefore all of the acrylonitrile which is not afiixed on the cellulose is. considered as lost. In the usual processes used in cyanoethylation where very large amounts of acrylonitrile are utilized, acrylonitrile which is not reacted can be recovered practically, and there the acrylonitrile ratio is determined only by the acrylonitrile permanently lost.

In the ordinary processes of cyanoethylation, the presence of various salts, such as sodium iodide, sodium thiocyanate and the like, which cause swelling of the cellulose, increase the rate of reaction markedly. In the process of the present invention, however, inferior products are obtained when such swelling salts are used. On the contrary, certain salts, such as sodium chloride or sodium tripolyphosphate which do not cause swelling have a beneficial elf ct when maximum cyanoethylation is desired.

The invention will be described in greater detail in conjunction with the specific examples in which the parts are by weight unless otherwise specified, and which are illustrated by the drawings in which:

Fig. l is a graph showing variation of cyanoethylation and AN ratio with the proportion of caustic alkali to cellulose;

Fig. 2 is a graph of variation of cyanoethylation with ratio of acrylonitrile to caustic soda for two concentrations of the latter;

Fig. 3 is a graph showing variation of degree of cyanoethylation with caustic soda concentration, and

Fig. 4 shows two graphs of the, degree of cyanoethylation with time for baths with and without non-swelling salts.

In the examples where tensile strength figures are given, they were obtained on a Scott inclined plane tester No. 2 under conditions of relative humidity and at a temperature of 21 C.

Example. 1

Cotton yarn was treated with a solution of 10% aqueous NaOH and acrylonitrilefor four hours at 15-20' C. The experiment was on a laboratory scale. The ratio of NaOH to cotton Was 10 and the ratio of cotton to acrylonitrile was 1.5. After the reaction was complete,

it was stopped by neutralizing with dilute acetic acid. The yarn was washed free of electrolytes and showed a 4.8% nitrogen and an AN ratio of 2.2. The tensile strength per denier was 720 grams.

When the above process was repeated with a weight ratio of caustic soda solution to cotton of 20 instead of 10, which corresponds to Example of the Miller and Flowers patent, a product was obtained containing 3.5% nitrogen. The AN ratio was 3.5 but the tensile strength was only 425 grams, which is inadequate for practical use.

The procedure of the example was repeated with other ratios of aqueous caustic soda to cotton going as low as 5:1. Cyanoethylation degree as measured by percent nitrogen and AN ratio is shown on Fig. 1. It will be noted that decreasing ratio of caustic soda to cotton caused an increase in cyanoethylation and a decrease in AN ratio, both being substantially linear. 'While an excellent AN ratio was obtained when only 5 times as much aqueous caustic soda was used as cotton, this procedure is not practical because the amount of liquid is insufiicient to permit uniform action, a ratio of 8:1 being the minimum for practical results. This lower limit, therefore, is dictated not by chemical considerations but by mechanical process handling.

The tensile strength at intermediate points was 610 grams for a 14:1 ratio and 655 for a 12:1 ratio.

Example 2 The procedure of Example 1 was repeated but only half as much acrylonitrile was used, i. e., cotton to acrylonitrile ratio of 3. The product showed 2.8% nitrogen and an AN ratio of 1.9 and a tensile strength of 585 grams. It will be noted that this product had a barely useful nitrogen content and tensile strength but showed a remarkably low AN ratio. It represents about as little acrylonitrile as can be practically used.

Other proportions of acrylonitrile to caustic soda were also used, and a series was run with 12% aqueous sodium hydroxide, in which case a shorter time, 2 hours, was used. The results are shown in Figure 2, the AN ratio remaining constant at 2.1 to 2.2 for the various runs with 10% sodium hydroxide and from 1.5 to 1.8 with the shorter time and 12% sodium hydroxide.

Example 3 Example 4 The effect of a non-swelling salt was determined by repeating-the conditions of Example 1 except that the ratio of cotton to acrylonitrile was 122.5, one series of runs being with 10% sodium chloride added and the other with no sodium chloride. The results are shown in Fig. 4. It will be apparent that up to about 2 hours there was no substantial difference between the two processes. With longer time, however, the process using only sodium hydroxide showed no increase in cyanoethylation, thus indicating that the reaction had reached a maximum.

With the sodium chloride the reaction continued up to 4 hours and resulted in a cyanoethylation approximately 50% greater than that obtainable at 2 hours.

When sodium tripolyphosphate is used in place of sodium chloride, the results are substantially similar to those shown above, and increased cyanoethylation is obtained when the time is extended.

Example 5 Mols- Tensile Tensile, Elongaturc Strength Re- Strength, tion, Regain, talned after 48 Grams Percent Percent hrs. at 0.,

Percent Cyanoethylated 670 7.5 6. 7 475 71% Cotton 3.9% N. Retained. Untreated Control..- 550 6.0 7.8 203 37%.

It will be apparent that there is a marked increase in tensile strength, a moderate increase in elongation and a slight decrease in moisture regain, less than for cyanoethylated cotton prepared by normal means. After 48 hours at the high temperature, the percent of tensile strength retained was almost double for the cyanoethylated cotton.

The cyanoethylated cotton and untreated control described above were also buried for two weeks in a soil containing virulent cellulose degrading microorganisms. At the end of that period the control had lost all of its tensile strength, being practically destroyed, whereas the cyanoethylated material still retained the tensile strength of 195. In other words, the cyanoethylated material prepared by the above example, while not completely mildewproof showed a greater degree of resistance to the attack by microorganisms than the uncyanoethylated cotton.

In the preceding examples sodium hydroxide has been used as the caustic alkali. This is preferred both because of the lower price of sodium hydroxide and because the properties are slightly better than when corresponding amounts of potassium hydroxide are used. However, since it is possible to use potassium hydroxide, the invention is not broadly limited to the use of the preferred sodium hydroxide.

I claim:

1. A process of cyanoethylating cotton textile fibers which comprises contacting the said fibers with an aqueous caustic alkali bath containing acrylontrile and from 8% to 12% of caustic alkali, the amount of aqueous alkali being from 8 to 14 times the weight of the cotton fiber and the ratio of acrylonitrile to the cotton fibers, by weight, being between 1:1 and 1:4, and maintaining the cotton fibers in contact with said aqueous bath at a temperature between 10 and 20 C. until a cyanoethylated cotton containing from 2.8% to 5.0% nitrogen by weight is obtained.

2. The process of claim 1 in which the caustic alkali is sodium hydroxide.

References Cited in the file of this patent UNITED STATES PATENTS 2,439,865 Roberts Apr. 20, 1948 2,473,308 Stallings June 14, 1949 2,535,690 Miller Dec. 26, 1950 FOREIGN PATENTS 588,751 Great Britain June 2, 1947 633,807 Great Britain Dec. 30, 1949 OTHER REFERENCES Daul: Textile Research Journal, March 1955, pp. 246- 253. 

1. A PROCESS OF CYANOETHYLATING COTTON TEXTILE FIBERS WHICH COMPRISES CONTACTING THE SAID FIBERS WITH AN AQUEOUS CAUTIC ALKALI BATH CONTAINING ACRYLONITRILE AND FROM 8% TO 12% OF CAUSTIC ALKALI, THE AMOUNT OF AQUEOUS ALKALI BEING FROM 8 TO 14 TIMES THE WEIGHT OF THE COTTON FIBER AND THE RATIO OF ACRYLONITRILE TO THE COTTON FIBERS, BY WEIGHT, BEING BETWEEN 1:1 AND 1:4, AND MAINTAINING THE COTTON FIBERS IN CONTACT WITH SAID AQUEOUS BATH AT A TEMPERATURE BETWEEN 10* AND 20*C. UNTIL A CYANOETHYLATED COTTON CONTAINING FROM 2.8% TO 5.0% NITROGEN BY WEIGHT IS OBTAINED. 